The invention relates to the production of tissue paper, finding application, for example, as kitchen towels, paper handkerchiefs, facials, toilet tissue, napkins and the like.
A wide variety of methods and machines is known with which such tissue papers can be produced in the sense of a more textile-like character, good absorptivity, especially good wet and dry tear strength, softness and the like, all of which require no detailing. Reference is made, however, to the German laid-open patent DE-OS 1 461 082 describing a method of making tissue paper having zones differing in basis weight. To block dewatering a modeling wire is placed on the dewatering wire. Both wires have the same extensibility and same roller guidance. The product produced therewith contains, in addition to the sheeting, a structure embossed by the modeling wire, resulting in comparatively sharply defined areas differing in basis weight. The fibers are oriented in the tissue paper with no preferential direction. When crumpled in use, tissue paper having conventionally a homogenous basis weight over its full surface area forms comparatively long creases which present added resistance to the deforming force.
The invention is based on the technical problem (objective) of providing a machine and a method permitting the achievement of tissue paper having enhanced visual and haptic properties.
With the achievement in accordance with the invention a tissue paper can now be produced which by creating structures of a textile nature conveys an improved visual appearance and xe2x80x9chaptic impressionxe2x80x9d, meaning the impression imparted subjectively as sensed by the fingers, i.e. the xe2x80x9cfeelxe2x80x9d. What is appreciated particularly is a good combination of surface softness and crumple softness. This is achieved by forming a tissue paper textured in small areas of elevated and diminished basis weight in the macro range. The areas of diminished basis weight offer less resistance to a deforming force than the areas of elevated basis weight in thus shortening the length of the creases resulting from crumpling. The meaning of this is enhanced crumple softness both physically and sensorically.
It is via the closed wire zones or wire mesh of the backing texturing wire that dewatering by the sheet-forming wire in the Z direction is inhibited or strongly restricted, resulting in an added fiber concentration in the zones of unrestricted dewatering.
In the tissue paper product a comparatively vapid transition materializes between areas of high basis weight and areas of lower basis weight which is to be evaluated positive as regards the visual appearance of the product without having any negative effect on the enhanced crumple softness intended. The zones differing in basis weight that form substantially the sole structuring feature. The fibers in the tissue paper permit identifying an orientation in the machining direction. All conventional materials can come into consideration for the wires, e.g. metal-wire or plastics wires. One objective of the invention is to produce sheet paper not taking on the structure of the wire contacting the paper.
Further advantageous aspects read from the sub-claims. If the backing wire structure is designed so that the backing texturizing wire can be mechanically (preferably hydraulically) lifted from the dewatering and sheet-forming wire, the machine is able to produce standard tissue in addition to texturized tissue paper without any conversion whatsoever.
The backing texturizing wire, due to the texture and the wire itself, naturally reduces the overall dewatering capacity and should thus be patterned as coarse as possible to minimize detrimenting the dewatering capacity by the backing texturizing wire itself.
The fineness of the texture in the tissue paper, consisting of areas differing in basis weight, is limited to the extent with which blockage of dewatering (due to the texture of the second wire) in the Z direction is side-stepped by the water transport within the sheet-forming wire in the X-Y direction. For as fine a texture as possible in the tissue paper the dewatering wire needs to be selected as thin as possible (low water transport in the X and Y direction). The wires have a wire gauge of 0.1 to 0.4 mm. To avoid lengthy water transport in the X and Y direction a wire gauge smaller than 0.3 mm should be employed, smaller than 0.2 mm being even better. It is best to employ a wire gauge smaller than 0.1 mm.
In case the dewatering zones are interconnected in the texturizing wire, the zones of elevated basis weight in the tissue paper are interconnected netted. The resulting influence on the strengths is relatively slight or none at all. The texturizing wires producing paper with netted zones of elevated basis weight may also be belts in which the supporting fabric is supplemented by some other material which is structured on the side coming into contact with the paper, examples of which read from EP 0 135 231 B (producing cushions with elevated basis weight) and WO 93/0047A (producing a continuous net with elevated basis weight).
In case the wire zones of blocked dewatering in the texturizing wire are interconnected, a tissue paper materializes having joined zones of diminished basis weight, resulting in strengths being detrimented. In this case, use can also be made e.g. of a perforated film, belt etc. in addition to a coarse wire having a closed mesh texture in the concrete design. Due to the relatively small dewatering zones in the joined zones of diminished basis weight the stock concentration is high. This results in a xe2x80x9ccushioning effectxe2x80x9d positively influencing the thickness and absorptivity of multi-ply products (e.g. as the middle ply in three-ply kitchen towel, as the bottom ply in two-ply products, the side with the cushioning facing inwards).